The present invention relates to the field of optical wireless communications, also referred to as Free Space Optical Communications (FSOC). FSOC systems are today employed in military, civil, and commercial applications. An FSOC system generally consists of a set of two transmitting terminals and receiving terminals. A transmitting terminal transmits an optical signal generated by a (presumably electronic) source that converts electrical signals to optical signals for transmission out of the transmitting telescope. The receiving terminal receives the incoming optical signal into a receiving telescope, which focuses the signal into an optical focal plane for coupling into a photodetector, which converts the light energy into an electrical signal.
Pointing and steering of optical beams that either enter or exit from the focal plane of a telescope is typically carried out via motorized beam steering mechanisms, such as gimbals, mirrors or other techniques that guide the beam through the telescope from the focal plane to the optical detection circuit and from the optical transmission devices. Maintaining accurate alignment of the beam is essential for FSOC systems. This alignment requires fast responses to changes in the beam path and beam quality deriving from a range of sources including atmospheric effects and base mount motion. In order to account for beam perturbations due to atmospheric effects, very high angular positioning resolution and bandwidth is required in order for the receiver telescope to efficiently collect the incoming optical beam regardless of atmospheric conditions.
Conversely, the transmitter telescope must be able to quickly and accurately adjust the pointing of its beam so that it continuously remains directed onto a receiving terminal for detection by the terminal's photodetector. Changing atmospheric conditions will cause the optimal transmission angle to change with time even if both terminals are completely stationary. Thus a real-time control system is needed to sustain said optimal transmit/receive angle regardless of changing atmospheric conditions.
What is desired then is a beam tracking and pointing system that improves upon the accuracy and speed of existing tracking and pointing systems by providing high bandwidth and high angular resolution, and an associated control system to provide for rapid adaptation of the optical beam trajectory to compensate for changes in optical beam trajectory caused by variations and perturbations in the atmosphere, so that the light collecting apparatus in the FSOC focal plane receives a maximum optical power at all times and in all atmospheric conditions. The desired control system and beam steering devices would desirably possess the correct beam steering frequency response and optical intensity tracking response in order to provide an adaptable beam path to improve the optical intensity tracking capability.
References mentioned in this background section are not admitted to be prior art with respect to the present invention.